Page 294 - The Master Handbook Of Acoustics

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DIFFUSION OF SOUND

¨
BRUEL & KJAER

Relative sound pressure level - dB 10 dB

50 100 150 200 250
Frequency - Hz
FIGURE 13-1

Slowly swept sine-wave sound-transmission response of a 12,000-cu ft. video studio.
Fluctuations of this magnitude, which characterize the best of studios, are evidence of
nondiffusive conditions.

not perfectly diffused. A steady-state response such as this taken in an
anechoic room would still show variations, but of lower amplitude. A
very live room, such as a reverberation chamber, would show even
greater variations.
Figure 13-1 illustrates one way to obtain the steady-state response of
a room. Another is to traverse the microphone while holding the loud-
speaker frequency constant. Both methods reveal the same deviations
from a truly homogeneous sound field. Thus, we see that Randall and
Ward’s criteria of negligible frequency and spatial irregularities are not
met in the studio of Fig. 13-1 or, in fact, in any practical recording studio.

Decay Beats

By referring to Chap. 7, Fig. 7-10, we can compare the smoothness of
the reverberation decay for the eight octaves from 63 Hz to 8 kHz. In